1. Field of the invention
The present invention relates to a method for improving film quality of silica-based films, and more particularly it is concerned with a method for improving film quality, that can improve the denseness and etching resistance of a silica-based film formed by coating on the surface of a substrate.
2. Description of the prior art
Silica-based films, the uses of which over recent years have over a great variety of purposes, are used in, for example, surface stabilizing films or layer insulation films of semiconductor devices; insulation films or orientation films of liquid crystal devices; and surface protective films for ceramics, plastics or metals.
The properties required in the silica-based films used for such purposes are such that the films are uniform as being free from any defects such as pinholes or cracks, have superior mechanical strength, and have superior chemical resistance and moisture resistance.
Of these properties, particularly the mechanical strength, chemical resistance and moisture resistance are known to be greatly affected by the denseness of the silica-based films themselves, and this denseness can be evaluated generally on the basis of increase in the refractive index of a film or decrease in the rate of film loss by etching treatment. There has been hitherto proposed a method in which a silica-based film is subjected to a heat treatment at a relatively high temperature of about 750.degree. C. after coating in order to improve the denseness of the silica-based films (Japanese Pat. Publication No. 37353/1977), and this heat treatment is carried out usually in an atmosphere of oxygen, nitrogen or air.
Also proposed is a method in which a silica-based film is merely exposed to ultraviolet rays in place of such a heat treatment (Proceedings of the 31th symposium on semiconductors and integrated and circuits technology, Tokyo, Nov. 3 to 4, 1986; The electrochemical Society of Japan, pp. 121-126, "LOW TEMPERATURE PLANALIZATION TECHNIQUE FOR MULTILAYER INTERCONNECTIONS IN GaAs LSI PROCESS").
The conventional methods set out in the above can densify the silica-based films to a certain extent, but still tend to produce pinholes and cracks and have a poor film properties, so that it can not satisfy the properties required in the silica-based films utilized in various electronic parts.